The present invention relates to a photosensitive resin composition, which comprises an alkali-soluble resin and specific type of photosensitive material and is sensitive to radiation ray such as ultraviolet ray, far ultraviolet ray, X-ray, electron beam, molecular beam, .gamma.-ray, synchrotron radiation ray, etc. Above all, the present invention relates to a photoresist, and in particular to a photoresist composition used for fine fabrication purpose and provided with high resolution and sensitivity, good preservation stability and having pattern of vertical shape.
The photoresist according to the present invention is coated on a semiconductor wafer or a substrate such as glass, ceramics, metal, etc. by spin coating method or roller coating method in thickness of 0.5 to 3 .mu.m. Then, it is heated and dried, and circuit pattern is printed through exposure mask by ultraviolet ray irradiation, and a positive image is obtained by development. Further, by etching this positive image as mask, it is possible to produce a pattern on the substrate. Typical applications include semiconductor manufacturing process of semiconductor such as IC, manufacture of circuit substrate such as liquid crystal or thermal head, and further, the other photo-fabrication process.
As the positive type photoresist compositions, compositions containing alkali-soluble resin and naphthoquinonediazide compound as photosensitive material is generally used. For example, "novolak type phenol resin/naphquinoneazide substitution compound" is disclosed in U.S. Pat. Nos. 3,666,473, 4,115,128, and 4,173,470, etc. Also, as the most typical composition, "novolak resin consisting of cresol-formaldehyde/trihydroxybenzophenone-1,2-naphthoquinonediazide sulfonic acid ester" is described in: L. F. Thompson: "Introduction to Microlithography" (ACS Publication, No. 2, 19, p. 112-121).
Novolak resin used as bonding agent is soluble in alkali aqueous solution without being swollen, and it is particularly useful for this purpose because it shows high resistance to plasma etching in case an image generated is used as a mask for etching. Naphthoquinonediazide compound used as photosensitive material acts by itself as a dissolution inhibitor to reduce alkali solubility of novolak resin. It has specific feature in that, when decomposed under light irradiation, it generates alkali-soluble substance and rather enhances alkali solubility of novolak resin. Because of such extensive property changes to light, it is particularly useful as a photosensitive material of positive type photoresist.
Under such circumstances, a wide variety of positive type photoresist containing novolak resin and naphquinoneazide type photosensitive material has been developed and used in practical application, and sufficient results have been attained in fabrication of linewidth up to 1.5 to 2 .mu.m.
However, integrated circuits with increasingly higher integration is now being produced, and it is necessary to fabricate ultra-fine pattern with linewidth of 1 .mu.m or less in the manufacturing process of semiconductor substrate such as ultra-LSI. In such applications, there are strong demands on a photoresist, which has high resolution, high reproducing accuracy of pattern for precisely transferring pattern of exposure mask, high sensitivity from viewpoint of high productivity, and excellent preservation stability.
In order to attain high resolution, it has been attempted to increase content of quinone-diazide photosensitive group. For example, Japanese Patent Publication Laid-Open 60-158440 describes a method using a photosensitive material containing high triester content. Also, Japanese Patent Publication 61-118744 discloses an attempt to increase the number of quinonediazide photosensitive group contained in a molecule of photosensitive material.
However, some of these photosensitive materials are insoluble in solvents commonly used, or, even when dissolved, deposition occurs during storage of photoresist composition, and this causes troubles in photo-fabrication process or device manufacturing process and reduces yield. To prevent the deposition of photosensitive material, Japanese Patent Publication Laid-Open 61-260239 describes a method to add an organic solvent with solubility parameter of 11 to 12. However, since solvents such as dimethylsulfoxide are used, the resist compositions have poor preservation stability, and sensitivity and resolution are subject to extensive changes as time elapses.
On the other hand, Japanese Patent Publication Laid-Open 64-76047 discloses 1,2-naphthoquinonediazide sulfonic acid ester of specific type of spirobiindan compound or spirobichroman compound as a photoresist with long-term preservation stability.
However, when the photosensitive materials with specific structure are used as photoresist, cross-section of pattern is not satisfactorily rectangular, and further modifications are needed.
As described above, conventional types of photoresist cannot meet the requirements for practical use.
To solve the above problems, it is an object of the present invention to provide a photoresist composition for manufacture of semiconductor device, such as:
(1) a photoresist composition having high resolution; PA1 (2) a photoresist composition for accurately reproducing mask dimension over wide range of photomask linewidth; PA1 (3) a photoresist composition capable to generate resist pattern with cross-sectional shape having high aspect ratio in linewidth pattern of 1 .mu.m or less; PA1 (4) a photoresist composition having wide development latitude; PA1 (5) a photoresist composition soluble in resist solvent commonly used and with excellent preservation stability without generating foreign objects even when stored for long time; PA1 (6) a photoresist composition for producing heat-resistant resist image; and PA1 (7) a photoresist composition for generating pattern with cross-section closer to rectangle.